A variety of hydraulic equipments using a hydraulic fluids such as a construction machine, an injection molding machine, a press machine, a crane and a machining center have been widely used. A variety of oils have been used in these hydraulic equipments (see, for instance, Patent Document 1 or 2).
Patent Document 1 discloses a hydraulic fluid for a vibration suppression damper that has bulk modulus of 1.3 or more, a viscosity index of 110 or more and a pour point of minus 25 degrees C. or less, and is specifically arranged to include poly α-olefin, polyol ester and polyether.
Patent Document 2 discloses a lubricating oil, e.g. a compressor oil, a turbine oil and a hydraulic fluid, that is used for a lubricating system requiring a large working load, and is arranged to include alkyl diphenyl and alkyl diphenyl ether.    Patent Document 1: JP-A-2000-119672    Patent Document 2: JP-A-6-200277